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Hello, boys

17 July 1999

By Jon Copley

IF YOU want to sneak into a harem, the best strategy is to dress up in drag.
At least, that’s the tactic favoured by male giant cuttlefish, which turn
transvestite to slip past other males guarding their mates.

Cuttlefish and their cousins octopuses and squid are masters of disguise,
transforming their colour, shape and texture to evade predators. The animals
also use these abilities in elaborate courtship displays. For instance, male
giant cuttlefish (Sepia apama) flash black and white stripes over their
bodies to attract the smaller, mottled females.

Large numbers of the cuttlefish gather to mate on rocky reefs at Spencer Gulf
in South Australia. Whilst watching the courtship behaviour of these animals,
Mark Norman of James Cook University in Townsville and Julian Finn of the
University of Tasmania in Hobart noticed that small males often tagged along
with breeding pairs in the guise of females. The males’ arms are usually fringed
with webs, but the smaller males can retract these to impersonate the females,
as well as adopting the female body colour and pattern.

When the larger male is tied up fending off other rivals, the sneaky male
reveals his true colours in an often successful attempt to woo the female.
Furthermore, if the larger male returns to find his paramour flirting with the
sneak, the smaller male can rapidly don female disguise again to avert the wrath
of the spurned male (Proceedings of the Royal Society B, vol 266, p
1347).

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It’s not just the cuttlefish that are fooled. The biologists also have a hard
time telling the impostors from the real females. “We have to follow them and
see when they change back,” says Norman and Finn’s colleague Tom Tregenza of the
University of Leeds, who studied their videos of the cuttlefish. He says that
although there are other male animals that mimic females, none can switch its
disguises on and off as easily.

The cuttlefish originally transformed itself as a means of camouflage and
only later turned to female impersonation, according to Tregenza. “Once you’ve
got those abilities, they start to come into play for something else.”

But it’s unclear whether the transvestite males are undersized or simply
younger than those they cuckold—later abandoning the strategy once they
are large enough to compete for mates openly. “The larger males don’t need
to—they can win contests with other males,” says Tregenza.

There may now be an evolutionary “arms race” between the males, the
researchers suggest. Larger males may be developing better ways of spotting the
impostors, while the smaller males may be refining their disguise to overcome
this. “Certainly there’s a potential pressure for the impersonation to get
better and better,” says Tregenza. As very little is known about the mating
behaviour of cuttlefish, octopus and squid in the wild, transvestism may turn
out to be more widespread under the waves than anyone realised.